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89c9aa491a
POSIX 2008 states that if the input for 'logb[f|l]' is a subnormal number it should be treated as if it were normalized. This means the implementation should calculate the log2 of the mantissa and add it to the subnormal exponent (-126 for float and -1022 for double and IBM long double). This patch takes care of that.
40 lines
1.0 KiB
C
40 lines
1.0 KiB
C
/* s_logbf.c -- float version of s_logb.c.
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* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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*/
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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#include <math.h>
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#include <math_private.h>
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float
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__logbf (float x)
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{
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int32_t ix, rix;
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GET_FLOAT_WORD (ix, x);
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ix &= 0x7fffffff; /* high |x| */
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if (ix == 0)
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return (float) -1.0 / fabsf (x);
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if (ix >= 0x7f800000)
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return x * x;
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if (__builtin_expect ((rix = ix >> 23) == 0, 0))
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{
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/* POSIX specifies that denormal number is treated as
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though it were normalized. */
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int m = (ix == 0) ? 0 : __builtin_clz (ix);
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return -126.0 + (float)(8 - m);
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}
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return (float) (rix - 127);
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}
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weak_alias (__logbf, logbf)
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